Thermoplastic polymers, such as, for example, polyamides or saturated polyesters (PET and PBT), have to be modified, either in order to be able to withstand impacts, in particular at low temperature, or in order to modify their flexural modulus. This modification consists in incorporating polyolefins or rubbers in the said thermoplastics. When polyolefins are incorporated in these thermoplastics, it is useful for these polyolefins to be crosslinked. This crosslinking is useful in order to obtain a high viscosity of this polyolefinic phase and therefore, for example, to promote the dispersion of these polyolefins in the thermoplastic matrix. This crosslinking can also be useful, for example, in order for the polyolefinic phase which contributes impact strength not to penalize the temperature behaviour and/or the thermal ageing of a polyamide.
U.S. Pat. No. 5,208,292 discloses PETs and PBTs modified by a mixture of functionalized polyolefins which react with one another. It concerns the reaction of an ethylene/alkyl acrylate/glycidyl methacrylate copolymer with an ethylene/alkyl acrylate/maleic anhydride copolymer. A catalyst is also added to promote this reaction. This catalyst is, for example, a tertiary amine or phosphines.
EP 400890 discloses PETs and PBTs comprising ethylene/alkyl acrylate/glycidyl methacrylate copolymers crosslinked by:                either diamines        or copolymers comprising maleic anhydride        or copolymers having OH functional groups        or diacids or ethylene/(meth)acrylic acid copolymers        or amino acids.        
EP 382539 discloses polyamides comprising ethylene/alkyl acrylate/maleic anhydride copolymers crosslinked by diamines or products having two OH functional groups.
These crosslinkings are sometimes inadequate or are not carried out reproducibly.